What’s the point of shower trays with 4 upstands?

[curium]

I’m looking for a shower tray for my bathroom, 1000 x 800 with 2 upstands but can only find trays with 0 or 4 upstands.

My understanding is that you tile over the upstands for additional protection against leaks. My tray will be against 2 walls so the additional upstands are redundant and may interfere with fitting the shower enclosure.

Why are trays in this size with 2 upstands not available?

 

[Madrab]

It's really about keeping water in tray. Guess it's must be easier to create a mould that's symmetrical rather than Asymmetrical

My understanding is that you tile over the upstands for additional protection against leaks

To me that's a side effect of upstands but to be honest it's really not needed. If the space has been prepped correctly and the tray has been installed properly then upstands are not required.